add benchmark for simplifying sort

Verify performance behavior of #1079. Case with two tags is
quite a bit slower with the simplification.

spectator-api/src/jmh/java/com/netflix/spectator/perf/ArrayTagSetSort.java

@@ -0,0 +1,174 @@
+/*
+ * Copyright 2014-2023 Netflix, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.netflix.spectator.perf;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.infra.Blackhole;
+
+import java.util.Arrays;
+
+/**
+ * <pre>
+ * sort1_single                     thrpt    5  231987417.092 ± 1461766.430   ops/s
+ * sort2_single                     thrpt    5  231390816.374 ± 2900091.223   ops/s
+ *
+ * sort1_two                        thrpt    5  127862169.706 ± 3004299.720   ops/s
+ * sort2_two                        thrpt    5  107286992.610 ±  499836.589   ops/s
+ *
+ * sort1_four                       thrpt    5   45448061.771 ±  214688.930   ops/s
+ * sort2_four                       thrpt    5   45801768.604 ±  399120.395   ops/s
+ *
+ * sort1_many                       thrpt    5    7013914.451 ±  476174.932   ops/s
+ * sort2_many                       thrpt    5    7093001.872 ±  136273.382   ops/s
+ * </pre>
+ */
+@State(Scope.Thread)
+public class ArrayTagSetSort {
+
+  private static void insertionSort1(String[] ts, int length) {
+    if (length == 4) {
+      // Two key/value pairs, swap if needed
+      if (ts[0].compareTo(ts[2]) > 0) {
+        // Swap key
+        String tmp = ts[0];
+        ts[0] = ts[2];
+        ts[2] = tmp;
+
+        // Swap value
+        tmp = ts[1];
+        ts[1] = ts[3];
+        ts[3] = tmp;
+      }
+    } else if (length > 4) {
+      // One entry is already sorted. Two entries handled above, for larger arrays
+      // use insertion sort.
+      for (int i = 2; i < length; i += 2) {
+        String k = ts[i];
+        String v = ts[i + 1];
+        int j = i - 2;
+        for (; j >= 0 && ts[j].compareTo(k) > 0; j -= 2) {
+          ts[j + 2] = ts[j];
+          ts[j + 3] = ts[j + 1];
+        }
+        ts[j + 2] = k;
+        ts[j + 3] = v;
+      }
+    }
+  }
+
+  private static void insertionSort2(String[] ts, int length) {
+    for (int i = 2; i < length; i += 2) {
+      String k = ts[i];
+      String v = ts[i + 1];
+      int j = i - 2;
+      for (; j >= 0 && ts[j].compareTo(k) > 0; j -= 2) {
+        ts[j + 2] = ts[j];
+        ts[j + 3] = ts[j + 1];
+      }
+      ts[j + 2] = k;
+      ts[j + 3] = v;
+    }
+  }
+
+  private final String[] tagsArraySingle = new String[] {
+        "country", "US"
+  };
+
+  private final String[] tagsArrayTwo = new String[] {
+         "status", "200",
+         "client", "ab"
+  };
+
+  private final String[] tagsArrayFour = new String[] {
+        "country", "US",
+         "device", "xbox",
+         "status", "200",
+         "client", "ab"
+  };
+
+  private final String[] tagsArrayMany = new String[] {
+          "nf.app", "test_app",
+      "nf.cluster", "test_app-main",
+          "nf.asg", "test_app-main-v042",
+        "nf.stack", "main",
+          "nf.ami", "ami-0987654321",
+       "nf.region", "us-east-1",
+         "nf.zone", "us-east-1e",
+         "nf.node", "i-1234567890",
+         "country", "US",
+          "device", "xbox",
+          "status", "200",
+          "client", "ab"
+  };
+
+  @Benchmark
+  public void sort1_single(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArraySingle, tagsArraySingle.length);
+    insertionSort1(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort2_single(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArraySingle, tagsArraySingle.length);
+    insertionSort2(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort1_two(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayTwo, tagsArrayTwo.length);
+    insertionSort1(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort2_two(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayTwo, tagsArrayTwo.length);
+    insertionSort2(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort1_four(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayFour, tagsArrayFour.length);
+    insertionSort1(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort2_four(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayFour, tagsArrayFour.length);
+    insertionSort2(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort1_many(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayMany, tagsArrayMany.length);
+    insertionSort1(tags, tags.length);
+    bh.consume(tags);
+  }
+
+  @Benchmark
+  public void sort2_many(Blackhole bh) {
+    String[] tags = Arrays.copyOf(tagsArrayMany, tagsArrayMany.length);
+    insertionSort2(tags, tags.length);
+    bh.consume(tags);
+  }
+}